This invention relates to methods and apparatus for the determination or monitoring of arousals that are indicative of an apneic or hypopneic episode. An xe2x80x9cA/H episodexe2x80x9d, as used hereafter, is to be understood as including both obstructive apneas (lack of breathing) or hypopneas (reduction in breathing) occurring during sleep.
People suffering from Obstructive Sleep Apnea (OSA) and related conditions experience many A/H episodes during sleep. The conventional treatment for OSA is the well known Continuous Positive Airway Pressure (CPAP) treatment. An A/H episode often has an associated arousal, which is a nervous system response to low blood oxygen level and/or high blood carbon dioxide level.
The condition of OSA normally is diagnosed by laboratory based polysomnography (PSG). PSG involves the measurement of sleep and respiratory variables including EEG, EOG, chin EMG, ECG, respiratory activity, nasal airflow, chest and abdominal movements, abdominal effort and oxygen saturation. The data gathered leads to a calculation of the Respiratory Disturbance Index (RDI) which is the average number of arousals per hour due to respiratory disturbance. PSG is uncomfortable for a patient due to the placement of numerous electrodes on the patient""s head or face and the wearing of a mask or nasal prongs. PSG is an expensive procedure and has the inconvenience of requiring the patient to attend a sleep clinic for a whole night requiring continuous technician attendance.
In the clinic, cortical arousals can be detected by measuring and interpreting, either automatically or by eye, changes in the patient""s EEG and EMG. Arousals are an important indicator of the amount and quality of sleep obtained by a patient and the degree of severity of the patient""s apneas.
To obtain a display of the EEG, electrodes must be attached to the patient""s head and the signals from these electrodes passed through high gain amplifiers before subsequent display and recording. This is often inconvenient and time consuming; the signals also can become distorted or disappear due to electrode dislodgement or other artefacts such as sweating. To detect an arousal, the EEG, once displayed, requires interpretation either visually by a skilled operator or automatically by a computer-based analysis system. Apart from the difficulties of attaining accurate EEG data, EEG apparatus also is relatively more expensive than much other biomedical apparatus.
EEG data on its own is not an accurate determination of the occurrence of A/H episodesxe2x80x94an arousal can be due to other factors as noted.
Prior art disclosures that form background information to the present invention include (a) R. Ferber, et al, xe2x80x9cASDA Standards of Practicexe2x80x94Portable Recording in the Assessment of Obstructive Sleep Apneaxe2x80x9d, Sleep, 17(4): 378-392, 1994; (b) L. FeriniStrambi, et al, xe2x80x9cHeart rate variability during sleep in snorers with and without obstructive sleep apneaxe2x80x9d, Chest, 102(4): 1023-7, Oct. 1992; and (c) C. Guilleminault, et al, xe2x80x9cA review of 50 children with obstructive sleep apnea syndromexe2x80x9d, Lung, 159:275-287, 1981.
It is an object of the present invention to overcome or at least ameliorate one or more of the problems with the prior art. In one preferred form the invention seeks to provide a method and apparatus for monitoring the occurrence of arousals due to A/H episodes. The invention in another broad form has as an object the determination of an index of sleep quality that can be used as a diagnostic indicator of a person suffering from conditions such as OSA. Yet further, the invention has as an object the provision of diagnostic apparatus for the recording the occurrence of A/H episodes. A preferred embodiment particularly contemplates detecting sympathetic arousals indicative of A/H episodes by signals derived from a patient which are easier to detect than by EEG, and by use of apparatus that is less costly than that for EEG.
It has been determined that the coincident occurrence of change in the sympathetic physiological variable of sweating and another physiological variable, or of a change in at least two sympathetic physiological variables not necessarily including sweating, is indicative of an arousal associated with an apneic or hypopneic episode.
Therefore, the invention discloses apparatus for monitoring the occurrence of arousals associated with apneic or hypopneic episodes, the apparatus comprising: sensor means for obtaining two or more signals from a patient, one signal representative of skin conductance and the other signals each representative of a physiological variable; and means for correlating said skin conductance signal and at least one other said signal, a coincident change in at least said skin conductance signal and said at least one other said signal being indicative of the occurrence of an arousal.
The correlation can be other than a correlation in the strict mathematical sense, including coincident visual inspection, logical ANDing, indicator voting or weighted sums relative to a threshold.
Preferably, the sensor means comprises electrodes attachable to a patient""s body. The signals derived from the electrodes can be signal-conditioned. Furthermore, the means for correlating includes data processing means. Each said signal can have an associated confidence level so that a weighting can be applied in the correlation.
The invention further discloses a method for monitoring the occurrence of arousals associated with apneic or hypopneic episodes, the method comprising the steps of: obtaining two or more signals from a patient, one signal representative of skin conductance and the other signals each representative of a physiological variable; correlating the skin conductance signal and at least one other said signal; and determining whether a coincident change in at least said skin conductance signal and said at least one other signal occurs as an indication of the occurrence of an arousal.
The changes in physiological states can include reduction in blood oxygen saturation, change in heart rate, change in skin conductance, change in skin temperature, increase in blood pressure and changes in breathing sounds.
The invention further discloses apparatus for the diagnosis of apneic or hypopneic episodes resulting in arousals, the apparatus comprising: sensor means for obtaining from a patient two or more signals, each signal representative of a physiological variable and including skin conductance; and means for correlating said two or more signals, one or more coincident changes in at least said skin conductance signal and one other said signal being indicative of an arousal associated with an apneic or hypopneic episode.
The invention yet further discloses a method for the diagnosis of apneic or hypopneic episodes resulting in arousals, the method comprising the steps of: obtaining two or more signals from a patient, each signal representative of a physiological variable and including skin conductance; storing said signals as a time sequence; following completion of obtaining said signals, correlating said two or more signals; and determining whether a coincident change in at least said skin conductance signal and one other said signal occurs as an indication of the occurrence of an arousal associated with an apneic or hypopneic episode.
The invention yet further discloses apparatus for the acquisition of data from a patient from which the diagnosis of apneic or hypopneic episodes resulting in arousals can be made, the apparatus comprising: sensor means for obtaining from the patient two or more signals, each signal representative of a physiological variable and including skin conductance; and a memory for storing said signals in a time sequence for subsequent correlation.
The invention yet further discloses a method for the determination for a patient of an index of sleep quality, the method comprising the steps of: obtaining two or more signals from the patient, each signal representative of a physiological variable; correlating said two or more signals; and recording instances where there is a coincident change in said correlated signals, the number of instances of coincidence being proportional to said index.
The invention yet further discloses apparatus for monitoring the occurrence of sympathetic arousals associated with apneic or hypopneic episodes, the apparatus comprising: sensor means for obtaining two or more signals from a patient, each signal representative of a sympathetic physiological variable; and means for correlating said two or more signals, a coincident change in at least two of said signals being indicative of the occurrence of a said arousal.
The invention yet further discloses a method for monitoring the occurrence of sympathetic arousals associated with apneic or hypopneic episodes, the method comprising the steps of obtaining two or more signals from a patient, each signal representative of a sympathetic physiological variable; and correlating said two or more signals whereby a coincident change in at least two of said signals is indicative of the occurrence of a said arousal.
Embodiments of the invention have the advantage of being non-invasive. This is of particular importance when diagnosis of conditions such as OSA must be undertaken on a baby or small child who may be disturbed by the conventional PSG apparatus.
One embodiment, relating to apparatus for the acquisition of data from which the diagnosis of apneic or hypopneic episodes, and thus the likelihood of the presence of conditions including OSA exist in a patient, can, in the first instance, substitute for a conventional sleep study and allow a candidate to collect data when in the home in a non-invasive manner. The data then can be analysed by a medical practitioner and a determination made of whether further detailed investigations need to be conducted.